In assembling integrated circuits, devices are formed on a semiconductor wafer using semiconductor processing. Once processed to a complete stage, the individual integrated circuit devices may be separated from one another or “singulated.” The individual devices may be referred to as “dies” or as “integrated circuit dies.” During completion of the semiconductor processes that form circuitry on the dies, terminals are formed for providing signal and power electrical connections to the circuitry within the dies. For example the dies may have aluminum bond pads or copper bond pads on an active surface, or “face,” of the device that are the terminals. Recent package types that provide packaged integrated circuits for surface mounting to a system board or module include “flip chip” on lead frame assemblies disposed within molded packages. In a flip chip integrated circuit package, the integrated circuit has posts or pillars formed on the bond pads on the active surface and extending away from the active surface of the die. The pillars may be of copper. Solder is formed on the ends of the pillars to form pillar bumps. The pillars are conductive and the pillar bumps form electrical connections to the bond pads.
The individual integrated circuits are then removed from the semiconductor wafer by singulation to form integrated circuit dies. In assembly, the integrated circuit dies are positioned so that the active surface of the integrated circuit device faces a surface of a package substrate, for example a lead frame, in a die mounting area. Conductors in the package substrate may have conductive lands that correspond to the pillar bumps for making electrical and physical connections to the die. The solder of the pillar bumps is bonded to the package substrate using a thermal reflow process. In the thermal reflow process, heat sufficient to melt the solder is applied. The solder reflows onto the substrate, for example a lead frame, and then forms solder joints that physically bond and electrically connect the integrated circuit die to the package substrate. Non-uniform sized posts or pillars and/or non-uniform solder thickness of solder material at the ends of the pillar bumps can create non-uniform bond line thicknesses in the solder joints formed during assembly of a packaged integrated circuit.